1. Field of the Invention
This invention relates to a method and apparatus for measuring the weight of a seat occupant and classifying the occupant into a weight class.
2. Related Art
Most vehicles include airbags and seatbelt restraint systems that work together to protect the driver and passengers from experiencing serious injuries due to high-speed collisions. It is important to control the deployment force of the airbags based on the size of the driver or the passenger. When an adult is seated on the vehicle seat, the airbag should be deployed in a normal manner. If there is an infant seat or small adult/child secured to the vehicle seat then the airbag should not be deployed or should be deployed at a significantly lower deployment force. One way to control the airbag deployment is to monitor the weight of the seat occupant.
Current systems for measuring the weight of a seat occupant are complex and expensive. These systems use various types of sensors and mounting configurations to determine seat occupant weight. For example, some systems use pressure sensitive foil mats or a plurality of individual sensors mounted within a seat bottom foam cushion while other systems mount sensors on seat tracks, seat frame members, or other seat structural members. The combined output from the sensors is used to determine the weight of the seat occupant. The accuracy of the weight measurements from these types of sensor systems can be compromised due to additional seat forces resulting from the occupant being secured to the seat with a seatbelt.
For example, weight sensor systems can have difficulty identifying an adult, a child, or a car seat when the seatbelt is being used. When a child seat is secured to a seat with a seatbelt, an excess force acts on the sensors mounted within the rear portion of the seat bottom, which interferes with accurate weight sensing. Over tightening of the seatbelt to securely hold the child seat in place, pulls the child seat down against the rear part of the seat bottom, causing the excessive force measured by the sensors. Due to this effect, the current weight sensing systems have difficulty in discerning between an adult belted to a seat and a child seat secured to the seat with a seatbelt.
In order to address this problem, sensors have been incorporated into the seatbelt to measure the tension force applied to the seatbelt as passengers or a child seat is secured to the seat. High seatbelt tension forces indicate that a child seat is secured to the seat. One disadvantage with current seat belt force sensors is that it is difficult to get accurate seat belt force measurements. Another disadvantage with current seat belt force sensors is that non-axial loading on the belt can affect the accuracy of the force measurement.
Once seat occupant weight force measurements and belt force measurements are taken, the seat occupant is typically classified into a predetermined classification. Some systems attempt to classify seat occupants into predetermined customer-specified classes usually based only on occupant weight. The classification information is then used to modify the deployment of the airbag. These systems do not provide accurate and consistent classification over a wide range of adverse road conditions and/or occupant seating conditions.
The accuracy of the weight measurements from known sensor systems can also be compromised due to variable seat forces resulting from momentary events such as rough road conditions or seat occupants adjusting seat position, for example. These types of events can transfer or remove weight from the seat for short periods of time, which affects the accuracy of the system.
Thus, it is desirable to have an improved seat occupant weight measurement and classification system that provides increased accuracy in weight measurement and classification as well as overcoming any other of the above referenced deficiencies with prior art systems.